1. Field of the Invention
The present invention relates generally to medical devices, and, in particular, to a system of improved irrigation and aspiration catheters used in the containment and removal of emboli resulting from therapeutic treatment of occlusions within blood vessels.
2. Description of Related Art
Human blood vessels often become occluded or blocked by plaque, thrombi, other deposits, or emboli which reduce the blood carrying capacity of the vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, and even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected.
Balloon angioplasty, and other transluminal medical treatments, are well-known, and have been proven efficacious in the treatment of stenotic lesions in blood vessels. The application of such medical procedure to certain blood vessels, however, has been limited, due to the risks associated with creation of emboli during the procedure. For example, angioplasty is not the currently preferred treatment for lesions in the carotid artery, because of the possibility of dislodging plaque from the lesion, which can enter the various arterial vessels of the brain and cause permanent brain damage. Instead, surgical procedures such as carotid endarterectomy are currently used, wherein the artery is split open and the blockage removed, but these procedures present substantial risks.
Other types of intervention for blocked vessels include atherectomy, deployment of stents, introduction of specific medication by infusion, and bypass surgery. Each of these methods are not without the risk of embolism caused by the dislodgement of the blocking material which then moves downstream. In addition, the size of the vessel may limit access to the vessel.
Thus, there is a need for a system to contain and remove such emboli. Various devices and methods have been proposed, but none have been especially commercially successful. Perhaps this is because a number of significant problems are faced in designing a system which will quickly and easily, yet effectively, evacuate emboli from a treatment location within a blood vessel. First, the small size of certain vessels in which such therapy occurs is a limiting factor in the design of emboli containment and removal systems. Vessels as small as 3 mm in diameter are quite commonly found in the coronary arteries, and even certain saphenous vein graph bypass vessels can also be as small as 3 mm or 4 mm; although some can range as high as 7 mm. Certain of the carotid arteries also can be as small as 4 mm in diameter; although, again, others are larger. Nevertheless, a successful emboli removal system must be effective within extremely small working areas. The system is equally effective in larger vessels, those of 5 mm or more in diameter.
Another obstacle is the wide variety in emboli dimensions. Although definitive studies are not available, it is believed that emboli may have approximate diameters ranging anywhere from tens of micrometers to a few hundred micrometers. More specifically, emboli which are considered dangerous to the patient may have diameters as large as 200 to 300 micrometers or even larger. Thus, an effective emboli removal system must be able to accommodate relatively large embolic particles and, at the same time, fit within relatively small vessels.
Another difficulty that must be overcome is the limited amount of time available to perform the emboli removal procedure. That is, it will be understood that in order to contain the emboli produced as a result of intravascular therapy, the vessel must be occluded, meaning that no blood perfuses through the vessel to the end organs. Although certain perfusion systems may exist or may be developed which would provide occlusion to emboli while permitting the substantial flow of blood, at present, the emboli may be contained only with a complete occlusion as to both blood flow and emboli escapement. Thus, again depending upon the end organ, the complete procedure, including time for the therapeutic treatment as well as exchanges of angioplastic balloons, stents, and the like, must be completed within just a few minutes. Thus, it would be difficult to include time for emboli removal as well. This is particularly true in the larger size vessels discussed above wherein a larger volume results in additional time required for emboli evacuation.
Moreover, it is important that an emboli containment and removal system be easy to use by physicians, and compatible with present therapeutic devices and methods. In addition, there are other difficulties which have made the successful commercialization of emboli containment and removal systems thus far virtually unobtainable.
The present invention advantageously satisfies the need in the prior art by providing a catheter system adapted to provide at least one pair of optimized paths for irrigation and aspiration fluid flow. Through careful design of the cross-sectional area of these paths, the present system is able to be compactly utilized in even the smaller size blood vessels. It can also be easily adapted to provide efficient and speedy emboli containment and evacuation in larger size vessels. This system is compatible with more common therapy devices in widespread use today, and is designed for rapid evacuation and ease of use.
It will be appreciated that, as used herein, the term xe2x80x9ccatheterxe2x80x9d is broadly used to refer to a number of medical instruments, including without limitation, guidewires, therapy catheters, and the like. Thus, it is important in the present invention that the medical instruments used therein cooperate together to define optimized paths for irrigation and aspiration, as set forth herein in more detail.
Thus, in one embodiment of the present system, at least two catheters are utilized to form and evacuate a treatment chamber. Again, however, it will be appreciated that the term xe2x80x9cchamberxe2x80x9d refers broadly to a treatment location or site where therapy is performed and emboli possibly produced. The catheters of the present invention telescope one in another in order to form a pair of irrigation and aspiration paths. An outer, larger diameter catheter forms the main body or housing for the system. An inner, smaller diameter catheter is positioned within the lumen of the outer or main catheter. An optional intermediate, or middle catheter is positioned over the inner catheter so as to be within the space formed between the inner and outer catheters. Thus, in this embodiment, the catheters cooperate to form two irrigation/aspiration paths: one between the outer catheter and intermediate catheter, and one between the intermediate catheter and inner catheter. In another embodiment, these paths are formed by the annulus between each pair of respective catheters of the present system; although it will be understood that, in use, the catheters may not necessarily be positioned concentric one with another. Therefore, the term xe2x80x9cannulusxe2x80x9d is used in a broader sense to refer to the path or space between any two catheters.
In addition, rather than being telescoped, the innermost two catheters may be placed side-by-side within the main catheter. In this embodiment, less frictional losses are experienced by the fluid as it flows in and out of the irrigation/aspiration paths. Moreover, the intermediate catheter may take the form of a dedicated irrigation catheter or, conversely, a dedicated aspiration catheter. Likewise, the intermediate catheter may comprise a therapy catheter which rides over the inner catheter (which itself may take the form as a typical guidewire) to the treatment site, or the therapy catheter can be built over an aspiration catheter to provide another embodiment of the intermediate catheter. Since irrigation or aspiration can take place in the path between the inner catheter and the therapy catheter, less time is incurred in the emboli removal process, since the therapy catheter need not be removed in exchange for other types of catheters.
Alternatively, the intermediate catheter can be a single main catheter configured to provide both irrigation and aspiration. This catheter has two lumens, one of which can extend past the distal end of the catheter. One lumen can be used to provide irrigation, while the other provides aspiration. This dual lumen catheter can be configured such that at least a portion of the catheter rides over the inner catheter. Alternatively, the catheter can comprise a rheolitic device, or any other device capable of both treating and aspirating the occlusion. This would eliminate the need for a separate aspiration catheter, thus simplifying the procedure.
In another embodiment, once therapy has been performed, the therapy catheter is removed, and the patient""s own blood acts as irrigation fluid. This eliminates the need for a separate irrigation catheter and irrigation fluid. Aspiration can occur through an aspiration catheter, or through the outer catheter. This reduces the time necessary to complete the procedure and reduces the number of necessary catheters.
Another aspect of the present invention is that the catheter system itself is provided with occlusive devices to form an emboli containment chamber. It will be noted that at least two such occlusive devices are needed to form a chamber in a straight vessel, while multiple occlusive devices may be necessary to provide emboli containment in the case of a branching vessel. Again, in this context, the term xe2x80x9cocclusive devicexe2x80x9d makes reference to the blocking or containment of emboli within the chamber, since perfusion systems which provide occlusion to the emboli are within the scope of the present invention. Thus, various types of occlusive devices such as filters or expandable braids that allow particles of less than 20 micrometers to pass through while preventing the passage of larger particles, and including inflatable or expendable balloons such as those which are employed by the present catheter system or otherwise, are within the scope of the present invention. In one preferred embodiment, the outer catheter comprises a main catheter having an occlusive balloon mounted on the outer diameter thereof. The occlusive balloon is inflated by means of an inflation lumen formed in a wall of the main catheter. The inner catheter comprises what may be referred to as a guidewire, but which is also hollow to provide an inflation lumen for a second occlusive balloon mounted at the distal section thereof. This occlusive balloon remains inflated until the guide catheter crosses the site of the lesion within the vessel. Thus, when inflated, these two occlusion balloons form an emboli containment chamber. The inner catheter provides a guidewire for those types of therapy devices which are in common use. One such catheter for a dedicated irrigation/aspiration catheter is positioned over the guidewire to form one of the irrigation/aspiration paths therewith.
Another advantage of the present invention is that the catheters are sized so as to optimize the cross-sectional area of the irrigation/aspiration paths. Thus, a larger range of emboli sizes are capable of being evacuated. Moreover, irrigation or aspiration is possible through either path, depending upon the desired conditions or particular procedure being performed. Thus, the versatility of the present system allows, in one embodiment, aspiration to be performed through the outer path and irrigation to be provided through the inner path, or vice versa. It will be noted for clarity that xe2x80x9couter pathxe2x80x9d refers to that formed between the outer catheter and the intermediate catheter, while xe2x80x9cinner pathxe2x80x9d refers to that formed between the inner catheter and intermediate catheter.
In another embodiment, the respective irrigation/aspiration cross-sectional areas are designed to balance and optimize flow. This balancing of the path areas not only allows the reversal of irrigation or aspiration, as explained above, but also improves the fluid mechanics exhibited by the system. That is, the flow of irrigation fluid within the vessel can be analogized to fluid flow within a pipe, with the entrance of the pipe being the mouth of the irrigation catheter and the exit of the pipe being the mouth of the aspiration catheter; it is the flow into the chamber versus the flow out of the chamber that creates the pressure within the chamber. Thus, a differential in pressure at the mouths of the irrigation and aspiration catheters will generate a flow rate used to evacuate the containment chamber. However, since flow rate varies with the product of fluid velocity in the cross-sectional area, for steady flow rate, it would be observed that decreases in the cross-sectional area of one of the irrigation/aspiration paths will produce an increase in fluid velocity. Since local pressure varies with the square velocity, such a reduced path cross-sectional area could produce an excessive pressure which may damage the vessel. Thus, it is desirable that local pressures in the vessel not exceed about 1.5 atmospheres (e.g., less than about 50 psi). In addition to possible damage, excessive pressures may simply cause the vessel to expand without resulting in any advantageous increase in flow rate. Thus, by optimizing the respective areas of the irrigation/aspiration paths, these parameters can be maintained within tolerable limits.
Increases in internal or local pressures also require substantial increases in external pressures. That is, in order to maintain the desired flow rates necessary to quickly and efficiently evacuate the containment chamber, as the cross-sectional area of the irrigation/aspiration paths are reduced, a greater change in pressure (xcex94p) is required to generate sufficient fluid velocity. Taking into consideration the frictional losses in the system, extremely high xcex94p""s may be required. Thus, it is important to maintain a balanced system so that excessive internal pressures are not produced, which may damage the vessel. Such pressures may also have the effect of causing a leak in the chamber.
Thus, the present invention provides a catheter system, comprising a hollow inner catheter having an occlusion device mounted on the distal end. At least a portion of an intermediate catheter is positioned over the inner catheter to create an inner fluid pathway for irrigation or aspiration. The intermediate catheter is slidable to a location proximal to the occlusion device on the inner catheter. A main catheter sized to receive the intermediate catheter such that an outer fluid pathway is formed therebetween for irrigation or aspiration. The main catheter also has an occlusion device mounted on its distal end which cooperates with the occlusion device on the inner catheter to form a chamber therebetween. The main catheter has an irrigation/aspiration port to permit irrigation or aspiration through its lumen. In one preferred embodiment, irrigation fluid is provided through the inner pathway and aspiration pressure is provided through the outer pathway.
The inner catheter is preferably a guidewire. The intermediate catheter can be an irrigation catheter, an aspiration catheter, a combined irrigation/aspiration catheter, or a therapy catheter, such as a drug delivery catheter, a laser, an ultrasound device, a thrombectomy catheter, a rheolitic device, a stent-deploying catheter, or any of a number of devices. The therapy catheter can be, for example, a balloon angioplasty catheter. Inflatable balloons can also be used as the occlusion devices on the inner and main catheters. To inflate the balloon, the main catheter can further comprise an inflation lumen located in the wall of the catheter in fluid communication with the inflatable balloon. The intermediate catheter can have both a main lumen and a separate lumen adjacent the main lumen sized to received the inner catheter slidably therein. The separate lumen can have a slit in an outside wall for insertion and removal of the inner catheter therethrough.
To fit in small blood vessels, it is preferred that the main catheter has an outer diameter of less than 5 mm. To provide efficient clearance of the emboli containment chamber, the inner pathway and the outer pathway should have an opening at their distal ends which act to balance fluid flows. In preferred embodiments, the inner pathway and the outer pathway each have an opening allowing the passage of particles of about 20 micrometers, up to those at least about 500 micrometers in diameter.
The system can include at least one additional inner catheter having an occlusion device mounted on its distal end sized to fit slidably within the intermediate catheter. This system can be used within branching blood vessels where more than one branch must be occluded to create an isolated chamber.
Accordingly, the catheter system of the present invention provides an improved emboli containment and removal system which can be utilized in a wide range of vessel diameters, including extremely small ones. The system is easy to use and can quickly and efficiently evacuate the treatment chamber.